There are already known various constructions of electrochemical cell devices; most if not all of which include a multitude of individual electrochemical cells that are arranged in groups or stacks. Depending on their intended use, such electrochemical cell devices fall in two categories: electrolysis cells in which water or another liquid substance is electrolytically dissociated into its components (oxygen and hydrogen when the substance is water), or fuel cells in which hydrogen or other gaseous fuel and oxygen are catalytically combined, usually in order to generate electricity in the process.
While these two kinds of electrochemical cell devices may be different in some respects, given the different tasks to be performed by them, they also have many features in common. As is well known, each cell of any such device includes an anode electrode plate, a cathode electrode plate, and an electrolyte confinement body (membrane or porous matrix) which contains a quantity of electrolyte or other ion transfer or exchange medium and is disposed at least between active areas of the anode and cathode electrode plates. To enable or enhance the electrochemical reaction, a layer containing a quantity of a catalyst, such as platinum, is typically present at each of the interfaces between the respective electrode plate and the electrolyte confinement body. An electrically conductive separator plate or a similar plate-shaped member (such as a cooling device) is usually interposed between the cathode and anode electrode plates of the respective adjacent cells to separate such cells from one another at least as far as fluid transfer therebetween is concerned.
When the electrochemical device is constructed and operated to perform electrolysis of water, water has to be supplied into the cell and to at least one of the active areas. In operation, electrolytic reaction takes place in the respective cell upon application of different electrical potentials to its electrode plates, resulting in the generation of product gases (hydrogen and oxygen) at the respective active areas of the respective electrode plates. Such gases have to be separately conducted away from such active areas and eventually separately discharged from the cell. On the other hand, when the device is to serve as an electric power generator, hydrogen (or another gaseous fuel) and oxygen (as such or as an ingredient of air) have to be separately admitted into the cell and separately distributed over the active areas of the anode and cathode electrode plates, respectively, whereupon an electrochemical reaction occurs resulting in the creation of an electrical potential difference between the anode and cathode electrode plates. This potential difference is utilized, in conjunction with that created in the other fuel cells arranged in the stack, to supply electric power to an external user device or circuit. The water that is formed in the cell as the reaction product must be conveyed away from the location at which it is produced and ultimately removed from the fuel cell.
It may be seen that, in each case, provisions have to be made not only for separate admission of the respective starting substance(s) to and discharge of the respective product(s) from the cathode and anode portions or sides of each of the cells, but also for substantially uniform distribution of each such substance over the respective active area and removal of each such product from all regions of the affected active area. The latter task is typically accomplished by providing at least those otherwise solid regions of the electrode plates which underlie the active areas with interconnected passageways that open onto the affected active areas and communicate with respective admission or discharge passages, such as by giving each of such regions a porous structure. Besides providing for an orderly management of flow of the various fluids toward or away from the active areas and providing electrically conductive paths between the active areas and the electrically conductive separator plates or similar plate-shaped components, this approach achieves a pronounced advantage of such electrode plate regions serving as supports for the electrolyte confinement body that prevent such body from buckling or other deformation that may adversely affect the operation or integrity of such a body and, consequently, of the electrochemical cell and/or device as a whole.
Especially when the electrochemical device is constructed to employ a solid electrolyte membrane as the electrolyte confinement body in each of its cells, it has to be operated at high, and often very high, superatmospheric pressures. While this requirement would not create any problems were the entire device (that is, both its interior and its exterior) subjected to only negligibly different pressures, for instance, by accommodating the device in a confining vessel and maintaining the pressure in the vessel around the device at the same level as, or at a level acceptably lower (or higher) than, that prevailing in the interior of the device, the provision of such a confining vessel significantly adds to the complexity and cost of the equipment and, moreover, considerably increases the overall dimensions and weight of the equipment, which makes this approach unsuited for use in applications where either the amount of available space, or the acceptable weight, or both, are either limited or at a premium.
On the other hand, when such pressure equalization measures cannot be taken, the existence of the pressure differential between the interior and the exterior of the electrochemical device imposes considerable strains on the peripheral portions of the individual cells and also puts high demands on the fluid impermeability of the various components of the electrochemical cell device and the interfaces therebetween.
To deal with the various requirements mentioned above, it has already been proposed to construct the electrode plates in such a manner that each of them includes a solid, fluid-impervious annular frame that constitutes the peripheral portion, and a fluid pervious (and electrically conductive) central portion that fills the space bounded by the frame. The interfaces between the frames are then properly sealed, usually by interposing discrete seals between such frames.
In at least one known cell construction employing these principles, each of the frames (as well as each of the intermediate separator plates or similar plate-shaped intermediate members) includes a plurality of through apertures or slots that are aligned, in the assembled condition of the electrochemical device, with corresponding slots or apertures of the other components to collectively constitute respective fluid supply and discharge conduits or manifolds. Moreover, it is necessary to provide individual connecting passages in each of the electrode plate frames to establish communication in the assembled device between the thus formed manifolds and the voids in the central portions of the appropriate ones of the electrode plates.
The making of such passages does not pose much of a problem when the frame is of a highly elastic material, especially a synthetic plastic material such as polyimide, inasmuch as the electrode plate or the frame can then be bent, without undergoing permanent deformation, out of the way to gain easy access to the respective portion of internal surface of the frame from which a material-removing operation such as drilling is to be conducted to form the respective passage leading to and terminating in the associated manifold.
Yet, despite the fact that there is a pronounced need or desire for operating electrochemical cell devices, especially those of the solid electrolyte type, at relatively high internal pressures, there is a limit to the pressure differential between the interior and the exterior of the device, beyond which materials of this kind are no longer suited for use. On the other hand, most if not all other materials that would satisfy the requirements put on them in the environment of such a device in all other respects while being additionally capable of withstanding higher pressure differentials, especially metallic materials, are not amenable to this passage forming expedient, so that other, more expensive, approaches would have to be used to produce such passages. Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide an electrochemical cell device including a stack of juxtaposed individual cells, which device does not possess the disadvantages of the known devices of this kind.
Still another object of the present invention is to devise an electrochemical cell device of the type here under consideration that would be capable of operation at a very high pressure differential between the interior and the exterior thereof.
It is yet another object of the present invention so to develop the electrochemical cell device of the above type as to assure easy and reliable assembly thereof and, when assembled and operated, the desired flow of the starting substance(s) and reaction product(s) between the respective manifolds and the respective internal regions of the device and proper distribution of the starting substance(s) to the active area(s) of the electrode(s).
A concomitant object of the present invention is to design the device of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.